Plastic dome

[kologha]

The Schatz Miniature 53 which I am repairing has a plastic dome, the original glass dome having been broken nearly 50 years ago. However the diameter of the dome it now has is a little on the large side with the result that it does not fit in the groove properly. If you position one side nicely in the groove, the other side rests on the outer rim of the groove. I was wondering if it were possible to shrink the base of the dome a little by, for instance, placing a large hose clamp (suitably padded) around the base and heating the bottom of the dome with hot water and then tightening the hose clamp a little and allowing the whole lot to cool down. One can do that with modern plastics but I don't know about plastics made in the 1960's. Any comments?

 

[sjaffe]

I can't imagine this working. Since this is an optical situation, unless you could get the circumference to decrease exactly uniformly, there would be undesired optical distortion. There are probably a host of other limitations that would make this approach impractical. If you have a hard limit restriction of having to reuse this dome, depending on the circumference/diameter difference between the dome and groove, you might consider if it is possible to make a very narrow strip that can be bent to a small enough diameter that is will fit in the groove and would nest within the dome. A piece of clear polycarbonate (Lexan) would offer the machinability/flexibility need. Another idea: maybe you could cut a clear circle of acrylic that had the inside diameter of the dome with cut outs for the movement support. The dome would nest over this and not slide around. Just throwing out ideas. Good luck,
Stan

 

[shutterbug]

You can still get glass domes. I'd go that route.

 

[kologha]

I like the idea of turning a ring to fit the groove but with a slightly larger diameter just above the groove to fit the dome. Probably the easiest solution. As far as importing a glass dome is concerned, it would be very expensive from SA and I doubt if the owner of the clock would agree to the extra cost. Many US sellers will not ship to SA and those that do charge very high shipping costs.

 

[AndyDWA]

We keep an eye out for cheap (free) quartz dome clocks as the glass domes on many of these fit nicely on the common 400-day clocks.